The present invention relates to fluid ejection devices, and more particularly to a plurality of barrier layers in a fluid ejection device.
Various inkjet printing arrangements are known in the art and include both thermally actuated printheads and mechanically actuated printheads. Thermal actuated printheads tend to use resistive elements or the like to achieve ink expulsion, while mechanically actuated printheads tend to use piezoelectric transducers or the like.
A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. A barrier layer is deposited over thin film layers on the substrate. The barrier layer defines firing chambers about each of the resistors, an orifice corresponding to each resistor, and an entrance or fluid channel to each firing chamber. Often, ink is provided through a slot in the substrate and flows through the fluid channel defined by the nozzle layer to the firing chamber. Actuation of a heater resistor by a xe2x80x9cfire signalxe2x80x9d causes ink in the corresponding firing chamber to be heated and expelled through the corresponding orifice.
Continued adhesion between the nozzle layer and the thin film layers is desired. With printhead substrate dies, especially those that are larger-sized or that have high aspect ratios, unwanted warpage, and thus nozzle layer delamination, may occur due to mechanical or thermal stresses. For example, often, the nozzle layer has a different coefficient of thermal expansion than that of the semiconductor substrate. The thermal stresses may lead to delamination of the nozzle layer, or other thin film layers, ultimately leading to ink leakage and/or electrical shorts. In an additional example, when the dies on the assembled wafer are separated, delamination may occur. In additional and/or alternative examples, the nozzle layer can undergo stresses due to nozzle layer shrinkage after curing of the layer, structural adhesive shrinkage during assembly of the nozzle layer, handling of the device, and thermal cycling of the fluid ejection device.
A fluid ejection device comprises a substrate having a first surface; a fluid ejector formed over the first surface; and a cover layer defining a firing chamber formed about the fluid ejector, and defining a nozzle over the firing chamber. The cover layer is formed by at least two SU8 layers.